The GRP78‐targeting peptide:siRNA complexes formed stably condensed ionic nanoparticles with calcium chloride (CaCl2) functioning as ionic stabilizer and additive that improved peptide‐based (siRNA) transfection efficiency and specificity in tumor (DU145) vs. non‐tumor (WI‐38) cells. The gene discussed is HSPA5; the disease is neoplasm.